I may be mistaken, but I think setting the type parameter to be abstract is
indeed the same as setting the field itself to be abstract. This snippet is
my evidence:
julia> abstract ABC
julia> immutable A <: ABC
a::Float32
end
julia> type B{T<:ABC}
a::T
end
julia> bA, bABC = B{A}(A(1)), B{ABC}(A(2))
(B{A}(A(1.0f0)),B{ABC}(A(2.0f0)))
julia> sizeof(bA), sizeof(bABC)
(4,8)
Even though both 'B' objects contain an 'A' immutable, bABC keeps it as a
pointer (size 8) whereas bA can directly unpack it into the definition.
On Thursday, February 4, 2016 at 1:59:17 PM UTC-5, Christopher Alexander
wrote:
>
> Oh cool! I was worried, since my call method was passing in the abstract
> type if none was specified (ie I wasn't setting a value for the param "a"),
> that it would just be the same as if I hadn't used a parametric type at all
> and just set the type of "a" to the abstract type.
>
> Thanks!
>
> Chris
>
> On Thursday, February 4, 2016 at 11:50:07 AM UTC-5, Kevin Squire wrote:
>>
>> No, `a` is the (concrete) type `T`, which is a subtype of `ABC` (and a
>> new type `B{T}` is created for each `T`). So you shouldn't lose
>> performance because of this.
>>
>> Cheers,
>> Kevin
>>
>> On Thu, Feb 4, 2016 at 8:10 AM, Christopher Alexander <[email protected]>
>> wrote:
>>
>>> Let's say I have the following types:
>>>
>>> abstract ABC
>>>
>>> type A <: ABC
>>> a::Float64
>>> end
>>>
>>> type B{T <: ABC}
>>> a::T
>>> end
>>>
>>> In some cases, I need for type "B" to be incompletely initialized so
>>> that I can define its parameter "a" later. I've found out that you can do
>>> something like this:
>>>
>>> type B{T <: ABC}
>>> a::T
>>>
>>> call(::Type{B}) = new{ABC}()
>>> end
>>>
>>> which then allows this:
>>>
>>> julia> myB = B()
>>> B{ABC}(#undef)
>>>
>>> My question is, I'm assuming you lose any of the performance gain by
>>> using the parametric type in this case because you are still using the
>>> abstract type "ABC" for the parameter "a" (even if you define it later with
>>> a concrete "A"). Is there a better way to do this?
>>>
>>> Thanks!
>>>
>>> Chris
>>>
>>
>>
